Hybrid Swarm Breeding

Definition

A hybrid swarm is a population of hybrids
which contains parent types, and offspring types, and
intermediate types all mingled together and
back-crossing and
cross pollinating each other. Hybrid swarms are
characterized by huge phenotypic differences
between individuals.

Uses

I use my hybrid swarms primarily as a source
for new breeding material. Secondarily I use them
as a means of preserving genetic diversity for
future breeding projects. I maintain hybrid swarms for
two species: Zea mays, and Cucumis melo. When I am
looking for a trait that could be incorporated
into a new variety or into an existing landrace I start
by screening the swarm. For example in the winter of
2010/2011 I planted huge numbers of corn swarm seed in the fall, and
several times during the winter, looking for seed that
grows well after being frozen in soil. Some plants survived
the frost and cold temperatures. After a couple of years of this treatment
they will be good candidates to incorporate into a
land-race of sugary enhanced sweet corn to add better
cold soil emergence to a variety that suffers severe
losses when planted in cold soil. An equally clever
result of these tests would be to find seeds that carry
perennial traits or are extremely frost tolerant.

Example

On my farm I maintain a few sweet corn populations,
and a popcorn population, and a flour corn population,
and a decorative corn population, and
a wild teosinte population. I also grow a hybrid swarm of
corn which contains genes from all of those populations and
many more. The only selection pressure that is put on this
population is that it must produce harvestable seed in my garden in spite
of my weeding habits, and the weather, and the soil, and the
pests, etc. If anything interesting shows up in the hybrid
swarm, it may be selected for further breeding work, or for
inclusion into one of my
landrace populations.
My landraces undergo selection to
conform to a set of expectations about how the plant should
grow, or look, or yield, or taste, etc. My hybrid swarm only has to
reproduce in my garden, and seed is saved from every plant that
successfully reproduces.

Problems

The genetic and phenotypic differences in a hybrid swarm can be
huge, even to the point of causing incompatibility
issues. For example my corn swarm contains parents
from the tropics which are day-length sensitive and
long season, and it also contains northern flints
which are very short season and mature regardless
of day-length. Staggering planting times, and
hand pollination can help to bridge some of these
differences. Natural or assisted back-crossing to intermediate
types can help create a genetic bridge between phenotypes.